The invention relates to a method for controlling the brightness in a manner independent of color and/or for controlling the color temperature in a manner independent of brightness for a microscope illumination system, as well as to an apparatus for carrying out the method.
In illumination apparatuses which exhibit an incandescent lamp, it is known for the brightness of the light emitted by a light source to be controlled by the lamp voltage being altered by means of an electrical circuit. However, control of the lamp voltage involves the disadvantage that the color temperature of the illumination light is altered at the same time thereby. A photographic exposure is possible under these light conditions only if chromatic defects in the subsequent photographic image are tolerated.
German Patent Publications DE-OS 2,757,543 and DE-UM 8,802,996 disclose apparatuses which preclude these defects. Both apparatuses exhibit a light source, a condenser system and an annular light guide. To control the illumination intensity, in DE-OS 2,757,543 a diaphragm slide is provided, which can be partially inserted into the illumination beam path between the individual condensers and thus covers a part of the beam. In DE-UM 8,802,996, to control the illumination intensity an opaque and displaceably arranged carrier with various perforated rasters is provided in front of the light entrance surface of the light guide. Since the light guide is designed to be homogeneous in its interior, the light exit surface of the light guide exhibits a uniform light intensity distribution. With such illumination apparatuses, control of the illumination intensity without alteration of the color temperature of the light is possible. However, it is disadvantageous that, besides a considerable expenditure on precision mechanisms, the total illumination intensity is also reduced by the light guide.
German Patent Publication DE-OS 2,745,397 discloses a light controller for light guide lamps with a multiplicity of individual fibers. To this end, a diaphragm made from a plurality of circular-sector surfaces is disposed in the illumination beam path between the lamp and the light entrance surface of the light guide.
To control the illumination intensity, these circular-sector surfaces are displaced with a handle relative to one another in such a manner that the illumination beam is cut asymmetrically in a disadvantageous manner. Furthermore, the region of high attenuation factors may be set only imprecisely.
German patent Publication DE-OS 2,701,764 discloses a light flux controller for controlling the brightness of illumination apparatuses for microscopes. This controller exhibits a carrier and a stationary family, disposed in the direction of the light, of light-transmitting channels. The carrier is disposed to be pivotable in the illumination beam path by means of a swivel apparatus. However, this apparatus is of very large dimensions and requires, as a result of the swivel apparatus, additional space in the illumination beam path of the microscope.